146 
The Worlt of the Geological Survey. 
a story of the profoundest interest, inasmuch as it dovetailed with 
the history of the human occupation of the country. In the second 
place, it was recognised that in many various ways these surface- 
deposits had a direct and vital influence upon the welfare of the 
population. In agriculture, in water-supply, in questions of drain- 
age and of the location of dwellings, it was seen that a knowledge 
of the soils and subsoils, and of the formations from which these are 
derived, was of the utmost practical importance. It was therefore 
determined that thenceforth the Geological Survey should not only 
portray the lineaments of the solid earth, but trace out the drifts 
and other surface-deposits which, like a garment, overspread and 
conceal them. It was impossible at first to go back over the ground 
where the surface-geology had been omitted. But it was arranged 
that when the whole country had once been mapped those tracts 
should be re-examined wherein the superficial deposits had not been 
surveyed. And, in the meantime, over all new areas the survey 
was made complete by the tracing out both of the surface-deposits 
and of the older rocks below them. 
No one who has not given some personal study to the complicated 
details of surface-geology can realise the amount of labour which the 
mapping of them often involves. The distinctions between the 
various superficial deposits, though real, are sometimes slight, and as 
sections are frequently few and wide apart, and the deposits so 
often occur in irregular patches, the ground has to be traversed with 
a detailed scrutiny which is generally not required for the older 
rocks underneath. Viewed broadly, the superficial accumulations 
are grouped and mapped by the Survey in two leading series. 
First come those which have resulted from the decay of rocks in situ, 
and then those of which the materials have been transported into 
their present position. 
1. The first of these two series, in so far, at least, as it is capable 
of being mapped, is mainly confined to the extreme southern fringe 
of England. All over the three kingdoms, indeed, the weathering 
of rocks has for ages been in progress, and here and there, especially 
in the upland and mountainous districts, accumulations of rotted 
rock may be observed at the foot of the crags and on the slopes. But 
what can there be observed is only what has accumulated since the 
last glaciers and ice-sheets scraped the loose detritus off the surface 
to form parts of the great group of glacial deposits. South of a line, 
however, drawn from the mouth of the Severn to the mouth of the 
Thames this country seems never to have lain under a mantle of 
moving land-ice, nor beneath a sea covered with drifting ice, though 
fragmentary sheets of old marine gravels cap many of the plateaux, 
and traces of probable ice-transport are found on the south coast. 
The surface in this southern tract has thus been left undisturbed for 
a great length of time. Its rocks have slowly decayed and their 
debris has gradually accumulated above them with only such slight 
transport as may have been due to the washing of rain and the sift- 
ing of wind. We see the i-esults of this prolonged waste in the 
